How to choose LUKS encryption when installing RHEL 6?

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With the default RHEL 6 installer, how can I choose the LUKS encryption?
Afaik if I prepare the disk like
cryptsetup luksFormat -c cast5-cbc-plain -s 128 /dev/$DEVICE
could be the "fastest" encryption, but the installer only prompts for password, then later, at the partitioning it recognizes it as "unknown" partition.
(HowTos)